Healthnotes Newswire (May 13, 2004)

RP is a group of diseases that affect the back of the inner part of the eye, called the retina. The retina contains cells called rods and cones that receive and process visual images. Rods enable vision in lower light, while cones pick up colors and enable sharp vision. As these cells in the retina are damaged by RP, night blindness, tunnel vision, and eventually total blindness may occur. There are several forms of RP; most are the result of gene mutations. Diet, stress, and individual metabolism influence the severity of the disease.

DHA, which is found in high amounts in the rods and cones of the eye, is necessary for proper vision development. Fish oil is a rich dietary source of DHA. The body can make smaller amounts of DHA from another fatty acid called alpha-linolenic acid, which is found in vegetable sources like flaxseed oil, soybean oil, and canola oil. Animal studies have shown a relationship between blood levels of DHA and levels of DHA in the retina, suggesting that higher intake of DHA or alpha-linolenic acid might increase DHA concentrations in the retina. People with RP have lower levels of DHA in the blood than people without the disease.

The current study examined a form of the disease that only affects males (called X-linked RP) and assessed how DHA affects its progression. Forty-one people completed the four-year trial. The participants were randomly assigned to take either 400 mg of DHA from fish oil per day or a placebo. Vision and retinal health were assessed to determine the response to taking DHA.

The group that took DHA had DHA blood levels that were two-and-a-half times higher than the levels in the placebo group. Overall, the rate of disease progression was not statistically different between the two groups; however, among the group that took DHA, those people who had the highest DHA blood levels had a slower rate of disease progression. DHA also significantly reduced the rate of rod loss in boys younger than 12 years old, and preserved cone function in those who were 12 years or older.

The results of this new study are encouraging for people with RP, as some benefit was associated with taking DHA. The amount of DHA used in this study was relatively small; more than three times as much has been used to treat other diseases, such as rheumatoid arthritis and psoriasis. Further studies are warranted to see if better results can be obtained with larger amounts of DHA. Other studies have shown that taking vitamin A may slow the progression of RP.